ISSN: 2471-9315
Gi-Yong Lee, Kyoung-Mi Kang, Jin-Yang Baek, So-Hyun Kim and Soo-jin Yang
Chung-Ang University, Republic of Korea
Asia Pacific Foundation for Infectious Diseases (APFID), Republic of Korea
Posters & Accepted Abstracts: Appli Micro
Background: Although vancomycin (VAN) is one of the alternative for the treatment of methicillin-resistant S. aureus (MRSA) infections, the usage of VAN has resulted in the emergence of VAN-intermediate (VISA) or -resistant S. aureus (VRSA). Using an isogenic pair of sequence type (ST) 72 CA-MRSA isolates from the bloodstream of a VAN-treated patient who failed VAN therapy, we investigated potential relationships between the reduced vancomycin susceptibility and with: i) cross-resistance to daptomycin (DAP) and host defense cationic antimicrobial peptide (HD-CAP); ii) alterations in cell envelope phenotypes (i.e autolysis, membrane potential, surface positive charge); and iii) transcriptional profiles of genes associated with HD-CAP and DAP resistance. Methods: Strains: Previously well-characterized isogenic pair of VAN-susceptible & VAN-intermediate ST72- MRSA strains, VSSA303 and VISA072 (VAN MICs of 1 and 4 �?µg/ml, respectively). Autolysis assays: TritonX-100 induced autolysis assays. Daptomycin challenged Population analysis profiles Membrane potential: Daptomycin challenged flow cytometric analysis using the lipophilic dye DiOC5 HD-CAP susceptibility assays: 2h killing assays using 5 �?�?103 CFU S. aureus against polymyxin B (PMB), LL-37(human cathelicidin found in neutrophil and skin), BMAP(Bovine serum), K9CATH(). Surface charge: cytochrome c binding assays. Transcriptional expression: standard qRT-PCR. Results: The VISA strain, VISA072, showed enhanced surface positive charge and, in turn, exhibited significantly increased susceptibilities to DAP, PMB, and LL-37. Reductions in both autolysis rate and membrane potential were observed in VISA072 strain. Further, the VISA strain displayed altered expression profiles of mprF, dltA, and graRS genes compared to those of the VSSA strain. Conclusion: These results demonstrate that alterations in cell wall synthesis physiology, cell membrane potential, cell surface positive charge are associated with reduced VAN susceptibility in the ST72-VISA strain. Key words : Vancomycin-intermediate resistant S. aureus (VISA); daptomycin(DAP); host defense cationic antimicrobial peptides (HD-CAPs)